This invention relates to a method of inhibiting intimal hyperplasia. More particularly, the invention concerns a method for inhibiting intimal hyperplasia induced by arterial interventions by administering topically at the site and at the time of the vascular injury a blood coagulation inhibitor known as tissue factor pathway inhibitor (TFPI).
As used herein, intimal hyperplasia (also referred to as neointimal hyperplasia) refers to the proliferative response to a vascular injury consisting almost entirely, although not exclusively, of smooth muscle cells (SMCs) which form an intimal lesion on the luminal surface around the inner circumference of a blood vessel (intima) following an arterial intervention such as, e.g., angioplasty or endarterectomy. This tissue ingrowth gradually encroaching into the lumen of the blood vessel is the leading cause of restenosis. Hyperplasia occurs gradually over a period of days to several weeks following the arterial intervention, as distinguished from a thrombus, such as may occur in the circulating blood immediately at the time of intervention.
Note: various literature references on the following background information and on conventional surgical and laboratory procedures well known to the person skilled in the art and other such state-of-the-art techniques as used herein are indicated by numbers in parentheses and appended at the end of the specification, ie., (1) to (62). PA1 300,000 coronary artery bypass surgeries PA1 300,000 percutaneous transluminal coronary angioplasties PA1 200,000 carotid endarterectomies PA1 200,000 peripheral vascular bypass surgeries, and PA1 100,000 to 200,000 other invasive procedures which blast burn, or break the occlusive plague (e.g., peripheral arterial angioplasties, laser ablation, intravascular stents, See (1), (2) (3). PA1 (a) To show that the administration of TFPI acutely and topically applied to a laboratory rabbit model was able to prevent intimal hyperplasia after arterial interventions of several different types; and PA1 (b) To examine TFPI binding and the early sequence of events following a vascular anastomosis. PA1 angioplasty, e.g., balloon angioplasty, laser angioplasty, intravascular stents, which are exemplified herein by an animal model for balloon angioplasty; PA1 endarterectomy, illustrated herein by an animal model for intimectomy, and PA1 vascular anastomosis such as bypass graft and arteriovenous fistula.
It is estimated that well over one million arterial interventions are performed each year in the United States for the treatment of occlusive arterial disease. This includes over
The early results of these procedures are generally excellent. However, within six months to five years, over 50% of the treated arteries develop restenosis and require reintervention (4-17). Most develop restenosis within the first year. Consequently, in many clinics, up to 50% of the case load consists of secondary procedures as opposed to first interventions. Restenosis is the reoccurrence of stenosis (reduction of luminal diameter) following manipulation of the arterial wall during surgery.
The restenosis rate varies by procedure and location. Restenosis occurs in 40% to 60% of patients within six months after percutaneous transluminal coronary angioplasty (PTCA) (4-8). The incidence of restenosis after carotid endarterectomy is approximately 30% at five years (9). Saphenous vein aorta-to-coronary grafts have a restenosis rate of 30% at five years and 70% at ten years (10-14). Following femoropopliteal bypass with vein grafts, the restenosis rate is between 30-40% at five years, and when prosthetic bypass grafts are used, between 50-60% (15-17).
Intimal hyperplasia is the principal cause of restenosis following arterial interventions (18-20). Intimal hyperplasia is the result of a complex series of biological processes initiated by arterial injury followed by platelet aggregation and thrombus formation with a final pathway of smooth muscle cell migration and proliferation and extracellular matrix deposition. Platelets adhere and aggregate at the site of injury and release biologically active substances, the most important of which are platelet-derived growth factors (21).
Thrombosis occurs from activation of the coagulation pathways (22). It has been postulated that intimal hyperplasia production is driven by two principal mechanisms platelet activation with the release of platelet-derived growth factors, and activation of the coagulation cascade with thrombus formation, which also results in the release of biologically active substances which can contribute to smooth muscle cell proliferation (23-32). Platelet-derived growth factors and components of the coagulation cascade are known stimulants of smooth muscle-cell growth (33-38).
Antiplatelet agents (e.g. aspirin, arachidonic acid, prostacyclin), antibodies to platelet-derived growth factors, and antithrombotic agents (e.g. heparina low molecular weight heparins) are potent inhibitors of smooth muscle growth (47,49-55). However, clinical trials have shown little effect of these agents on the rate of restenosis (55-62). One can only speculate as to why clinical trials have failed thus far, but two explanations seem plausible.
First, the dose of the agent delivered to the site of injury may have been inadequate. For instance, although thrombocytopenia substantially inhibits intimal hyperplasia in animals, antiplatelet agents have been ineffective in humans it is likely that the dose of antiplatelet agents at the site of injury is inadequate to completely prevent platelet adhesion. Secondly the timing of the drug administration may be inappropriate. Most drugs are given after the injured vessel surface has been exposed to blood and the biological processes which lead to intimal hyperplasia have been initiated.
Tissue factor pathway inhibitor (TFPI) is a naturally occurring glycoprotein inhibitor of the extrinsic pathway of coagulation (39-42). TFPI has been shown to inhibit Factor Xa directly and together with Factor Xa bind and inhibit tissue factor VIIa (39,43).
The name, tissue factor pathway inhibitor (TFPI) has been accepted by the International Society on Thrombosis and Hemostasis, Jun. 30, 1991, Amsterdam. TFPI was previously known as lipoprotein-associated coagulation inhibitor (LACM) TFPI was first purified from a human hepatoma cell, Hep G2 as described by Broze and Miletich, Proc. Natl. Acad. Sci. USA 84, 1886-1890 (1987), and subsequently from human plasma as reported by Novotny et al., J. Biol. Chem. 264, 18832-18837 (1989); and Chang liver and SK hepatoma cells as disclosed by Wun et al., J. Biol. Chem. 265, 16096-16101 (1990). TFPI cDNA have been isolated from placental and endothelial cDNA libraries as described by Wun et al., J. Biol. Chem. 263, 6001-6004 (1988); and Girard et al., Thromb. Res. 55, 37-50 (1989). The primary amino acid sequence of TFPI, deduced from the cDNA sequence, shows that TFPI contains a highly negatively charged amino-terminus, three tandem Kunitz-type inhibitory domains, and a highly positively charged carboxyl terminus. The first Kunitz domain of TFPI is needed for the inhibition of the factor VII.sub.a /tissue factor complex, and the second Kunitz domain of TFPI is responsible for the inhibition of factor X.sub.a according to Girard et al., Nature 328, 518-520 (1989), while the function of the third Kunitz domain remains unknown. See also U.S. Pat. No. 5,106,833. TFPI is believed to function in vivo to limit the initiation of coagulation by forming an inert, quaternary factor X.sub.a : TFPI: factor VII.sub.a : tissue factor complex. Further background information on TFPI can be had by reference to the recent reviews by Rapaport, Blood 73, 359-365 (1989); and Broze et al., Biochemistry 29, 7539-7546 (1990).
Recombinant TFPI has been expressed as a glycosylated protein using mammalian cell hosts including mouse C127 cells as disclosed by Day et al., Blood 76, 1538-1545 (1990), baby hamster kidney cells as reported by Pedersen et al., J. Biol. Chem. 265, 16786-16793 (1990), Chinese hamster ovary cells and human SK hepatoma cells. The C127 TFPI has been used in animal studies and was shown to be effective in the inhibition of tissue factor-induced intravascular coagulation in rabbits according to Day et al., supra, and in the prevention of arterial reocclusion after thrombolysis in dogs as described by Haskel et al., Circulation 84, 821-827 (1991).
Recombinant TFPI also has been expressed as a non-glycosylated protein using E. coli host cells and obtaining a highly active TFPI by in vitro folding of the protein as described in U.S. Pat. No. 5,212,091, the disclosure of which is incorporated by reference herein. See also Wun et al., Thromb. Hemostas. 68, 54-59 (1992).
The cloning of the TFPI CDNA which encodes a 31,950-Dalton protein of 276-amino acid residues with three potential glycosylation sites is further described in Wun at al., U.S. Pat. No. 4,966,852, and allowed application Ser. No. 08/093,285, the disclosures of which are incorporated by reference herein.
Recently, TFPI obtained through recombinant DNA clones expressed in E. coli as disclosed in U.S. Pat. No. 5,212,091 has been described as useful for reducing the thrombogenicity of microvascular anastomoses. In the disclosed microvascular surgery, it was desired to keep a very small vessel open for a short time and apply the TFPI topically to prevent thrombus formation. See U.S. Pat. No. 5,276,015, the disclosure of which is incorporated herein by reference.
The use of TFPI for treatment of sepsis or septic shock and sepsis-associated disorders is described in recently published patent applications PCT WO 93/24143 and PCT WO 93/25230.
In a model of vascular thrombosis a single application of TFPI by local irrigation prior to blood reflow prevented platelet adhesion and arterial thrombotic occlusion as determined after 24 hours (44,45). However, that study determined only the inhibition in the formation of a platelet plug within 24 hours as distinguished from end-stage intimal hyperplasia.
Recently, it has been reported that specific inhibition of Factor Xa with recombinant antistatin (rATS) or tick anticoagulant peptide (rTAP) reduces intimal hyperplasia after balloon angioplasty (46,47).